The overall objective of our research is to identify new compounds which have the potential to become useful antiviral drugs and to investigate how promising compounds act at the cellular, molecular and biochemical level. Toward this end, we have derived by in vitro selection methods human cytomegalovirus (HCMV) and human immunodeficiency virus (HIV) strains which are resistant to active compounds. Using drug resistance as a marker, we are in the process of identifying which HCMV and HIV genes have mutated to produce drug resistant virus strains. Identification of such genes is providing detailed understanding of antiviral drug action. Furthermore, the proteins specified by the genes may be new targets for antiviral drugs. The specific objective requiring the use of GCG analysis software is to compare the sequence of the viral genes to related viral, mammalian, and prokaryotic genes to better understand the function of the viral gene and the action of new inhibitors.